Add a node registration to a directory service.

     REGISTER [DECNET] NODE node-name
         [ DIRECTORY_SERVICE dir-service ]
         [ SYNONYM synonym-name ]
         [ TOWERS {tower-set} ]
         [ PHASEIV_PREFIX addr-prefix ]
         [ REVERSE_DIRECTORY rev-dir-name ]
         [ SYNONYM_DIRECTORY syn-dir-name ]

 This is used when a new node is made available in the network, and the
 node registration needs to be added to a directory service to allow
 lookup by other nodes.